1903 HOLLOW DALE PL 2018-01-02 MF Import

•' 4 114161�fr •� Access will be taken from two points; Holly Road at the north to lot 4 (the existing liome) and from Hollow Dale Road to the south to the other three lots. The southerly access will be through a 30' private road easement via paved road. New impervious areas proposed will include a 20' wide paved access road and 3 future single family residences. The homes will average 1800-2000 square feet including sidewalks, garav,- apron, and patios. Gravel driveways will connect the private access to the hot s. Storm water calculation- ill be done using the SCS Hydrographic computer simulation. The King Cot. 'y software will provide the runoff peaks and volumes for 2, 10, and 100 year/24 rtour storms. A pond will detain the 100 year developed runoff volumes and release them at the 100 year pre -developed rates through an oil/water separator. Although Title 24 of the Snohomish County Drainage Code requires a 10 year detention, the more restrictive Washington State Department of Fisheries standards will be used. Those restrict the post developed runoff to the 2 year, 10 year, and 100 year pre -developed rates. Flooding southwest of the site will be reduced with the addtional detention. Water clarification will be enhanced by a grass lined roadside ditch in the private drive, pond residence time, a wet pond, and an oil/water separator at the outlet from the pond. A downstream visit was conducted 7/2/96 to determine potential drainage problems and/or drainage impacts from the proposed development. The downstream analysis included observation for items including: erosion, sedimentation, flooding, and/or potential flow restrictions. Westerly Drainage Course: A majority of the drainage from the proposed area of development is intercepted by a ditch along the westerly property line. The ditch cutlets into the Hollow Dale Place roadside ditch which turns west and passes through a sho• driveway culvert. The ditch is very little grade as it continues another 150' before entering a 12" concrete pipe and crosses south beneath Hollow Dale Road. The outlet from the 12" pipe could not be found within the quarry spall riprap near the south side of the road although a large local wetland obviously receives the storm drainage from the area. A home at 1919 Hollow Dale Place appears to have a potential for flooding due to a low finish floor elevation and potential poor drainage typical of wetland areas (this is substantiated according to County drainage complaint records), 5-800' farther to the southeast the wetland discharges into a tributary to Swamr Creek before continuing to the south. Rnt Omw Rejxnt PERC0096033 Rn9u 5/19/97 DRP